1. Field of the Invention
The present invention relates to a method and apparatus for fabricating thin films. More particularly, the present invention relates to a new thin-film fabrication method and thin-film fabrication apparatus that enables high quality, high efficiency production of high-function optical thin films that are particularly useful for wavelength-selectable transmitting films, reflecting films, nonlinear optical effect films, optoelectronic conversion apparatuses, photoconductive films, optical recording media, organic electroluminescence elements, image display apparatuses, spatial photomodulators and other such areas of optical technology, optoelectronics technology and the like.
2. Description of the Prior Art
Optical thin films having various types of compositions have been put to use in various fields of application. For example, there are optical thin films which use reflection functions and wavelength-selectable transmission utilizing light absorption or interference.
Especially in recent years, in optoelectronics fields utilizing laser light, considerable progress is being made into the development of optical thin films having high functions that differ from before, for high-speed multi-dimensional parallel processing of information using multiplicity of light, or nonlinear optical effects and the photoelectric effect.
As materials used to form such high-function optical thin films, attention has focused on organic optical materials. Numbers of studies are being pursued relating to methods of fabricating organic optical thin films using the organic optical materials. The following are examples of methods that are known.
(1) Wet Methods Using Solvents, Dispersions, or Developers
Coating methods such as the application method, blade coating method, roll coating method, spin coating method, dipping method and spray method; printing methods such as lithography, relief, intaglio, perforated plate, screen, and transfer printing; electrochemical methods such as electro-deposition, electro-polymerization, and micell electrolysis (see, for example, JP-A-63-243298); and other methods such as the Langmuir blow-jet method of using monomolecular films formed on water.
(2) Methods Using Reactions Into High-polymer Compounds, Such as Polymerization of Monomer Source Material
These methods include the casting method, reaction--injection--molding method, plasma polymerization method and photo-polymerization method.
(3) Methods Using Gas Molecules (vaporization by heating)
These methods include the sublimation transfer method, vapor deposition method, vacuum vapor deposition method, ion-beam method, sputtering method, plasma polymerization method and photo-polymerization method.
(4) Methods Utilizing Melting or Softening
These methods include the hot press method (see, for example, JP-A-4-99609), the injection molding method, the extrusion method, and the method of single crystallization of molten thin films.
However, the optical thin-films formed by all of these conventional fabrication methods are limited to a relatively simple composition and structure, and are not suitable for fabricating high-function organic optical thin-films allowing a higher level of fine structural control. For example, a material such as organic ionic crystal that has no melting point is decomposed by heating, and even if the material does have a melting point, it decomposes at the vaporization temperature, making it difficult to control such phenomena, or to realize high-function, organic optical thin-films based on such control.
In JP-A-6-306181 and JP-A-7-252671, the present inventors described one means for resolving such problems. Specifically, the disclosures described a method and apparatus for fabricating an organic optical thin-film by spraying an organic optical material in the form of a solvent or dispersion into a high-vacuum vessel to deposit the material onto a substrate, followed by heat treatment. This method made it possible to fabricate an optical thin-film with control of fine structures in the sub-micrometer range at temperatures far lower than the decomposition temperature of organic optical materials.
With the above-described prior-art method and apparatus for fabricating organic, optical thin films, cleaning of the surface of the substrate for deposition of the thin-film material had to be done outside the apparatus. However, in the course of moving the cleaned substrate to the thin-film fabrication apparatus, the effect of the cleaning was reduced by exposure to floating particulate matter and/or contaminating gases, reducing the strength of the adhesion between the thin film and the substrate. Moreover, when it was required to increase the durability of the fabricated thin film by sealing the film in a material that acted as a barrier to gases, the sealing also had to be done outside the fabrication apparatus.
Again, however, removal of the substrate from the apparatus exposed the substrate surface and surrounding portions to floating particulate matter and/or contaminating gases, reducing the effectiveness of the sealing process and decreasing the durability of the thin film.
Thus, the conventional thin-film fabrication method had inherent limitations with respect to the efficient fabrication of high-function thin films.
An object of the present invention is to overcome the above-described drawbacks of the prior art by providing a thin-film fabrication method and apparatus that enables more efficient fabrication of thin films that offer high durability, high adhesion to the substrate and a high level of control of microstructures without giving rise to heat-decomposition of the thin-film composition materials.